1. Field of The Invention
The present invention relates to an optical system supporting device. More particularly, the present invention is concerned with a supporting device suitable for supporting an optical system, such as an objective lens system, through which a light spot is projected on a data recording medium in an optical data recording and/or reproducing apparatus, such as an optical disk unit.
2. Discussion of Related Art
In the above type of optical system supporting device, it is necessary to drive up or down an optical element, such as an objective lens, in accordance with any vibration and inclination of, for example, the surface of the optical disk. Therefore, in the conventional device, a holding member that holds an objective lens is displaceably supported by a connecting member composed of, for example, a plurality of wire springs or the like, and driven and controlled in the focal and tracking directions by an electromagnetic coil. However, this driving system drives the lens in the two dimensional direction, i.e., either sideways or up and down, to thereby form a secondary vibration system. Thus, for attaining stable control, it is necessary to effectively suppress a primary resonance.
Therefore, for conducting a stable control, it has been proposed to provide a damping means on a supporting mechanism to thereby suppress the undesired resonance.
As one of the above-mentioned damping means, a gelatinous damping material may be mentioned.
If, instead of a damping material made of a rubber, a gelatinous damping material is applied to an edge of a linear wire spring genellary used as a supporting member in an optical system supporting device, simple coating of the edge with the gelatinous damping material results in sagging of the damping material, which causes a problem of dispersion in properties. Under such circumstances, for example, Japanese Patent Publication Laid-Open Specification No. 232824/1990 (Reference 1) discloses a device provided with having a gel-filled holding member. The structure of this device is summarized below.
In FIGS. 13A and 13B showing the structure of the conventional device, an objective lens 101 is fixed to a lens holder 102. Both ends of each of four metallic wires 103 arranged in parallel are soldered by solder 107 to a base substrate 105 fixed to a base 104 and a holder substrate 106 fixed to the lens holder 102. Thus, the lens holder 102 is supported to in a cantilever manner.
A damper case 108 having two holes forms a fixing part side in combination with the base 104. A gelatinous damping material 109 (which is a gel mainly composed of thermosetting or UV-curable silicone) is filled and held in these holes of the damper case 108. A pin 102a formed in a part of the lens holder 102 is inserted in the damping material 109.
Further, the above Reference 1 discloses another structure shown in FIGS. 14A and 14B. In this structure as well, a container type structure is used for holding the gelatinous damping material. The gelatinous damping material 109 is filled and held in the container type structure formed in a part of the lens holder 102, through which the wires 103 are arranged. Also, the gelatinous damping material 109 is filled and held in the container type structure formed in a part of the base 104, through which the wires 103 are arranged.
Moreover, as the damping means for the supporting member of the optical system supporting device, in addition to the gelatinous damping material, the use of a rubber and the like is well known as disclosed in, for example, Japanese Patent Publication Laid-Open specification No. 73426/1991 (Reference 2).
In the damping means for the supporting member in this Reference 2, a plate spring structure is used as shown in FIG. 15. A plate spring 201 is formed in a thickness of about 0.1 mm, which is of an almost linear shape excluding both ends of the main body thereof. Fixing parts 202 and 203 are provided in the vicinities of the both ends, respectively. In these fixing parts, holes 204 and 205 are formed for positioning in the fixing. Projecting parts 206 and 207 of the both ends are respectively soldered to the end of a focal or tracking coil and FPC for power supply to thereby supply power.
A spring part 208 is formed in the center of one fixing part 203 along the direction of the extension of the plate spring 201. A projecting part 209 projected in the direction of the extension of the plate spring 201 is formed on both sides of the spring part. Further, a projecting part 210 projected rectangularly to the direction of the extension of the plate spring 201 is formed on the tip of the spring part 208.
Further, a supporting part 211 tapered along the direction of the extension of the plate spring 201 is formed on the other fixing part 204 on its side of the direction of the extension of the plate spring 201. The supporting part 211 and the projecting part 210 are connected by a long spring part 212 therebetween so that almost the whole part of the plate spring 201 can be deformed with the spring part 208 in the focal and tracking directions.
A damper material 213 composed of a butyl rubber is provided on almost the whole parts in the vicinities of the spring part 208 and projecting parts 209 and 210 continuous from the one fixing part 203, almost the whole part in the vicinity of the supporting part 211 continuous from the other fixing part 204 and the whole part of the long spring part 212. The part of the damping material 213 corresponding to the long spring part 212 is formed so as to have a small width.
Therefore, in an optical data recording and/or reproducing device, the minimization and speed increase are essential for the realization of the higher performance therefor. Accordingly, it is highly demanded to render an optical system supporting device for use therein smaller and lighter.
However, in the constructions as shown in FIGS. 13 and 14 of the above Reference 1, the container type structure is required for holding the gelatinous damping material. When such a container type structure is provided on the holding member or the fixing member, this member becomes large. Further, when the holding member for the damping material is provided using another part, not only the number of parts is increased but also the optical system supporting device becomes large. Thus, the conventional constructions have a problem that the optical system supporting device or the movable part thereof becomes inevitably large, so that it is unattainable to render the device smaller and lighter.
In particular, when a higher damping performance is required for the device of FIG. 14, the only measure is to increase the length of the filling part for the damping material to thereby enlarge the contact area with the connecting member. This, however, causes the problems that the external shape of the device becomes large and the weight thereof increases. Further, it is difficult to independently set or alter the coefficient of damping alone.
For example, when the length of the filling part for the damping material is increased, this affects the effective length and movable range of the connecting member, etc. to thereby cause design freedom to be poor.
Further, in the device as disclosed in the Reference 2, the rubber damping material is generally integrally formed with the supporting member, using a mold. On the other hand, the gelatinous damping material is immobilized by first potting the same at an appropriate site of the supporting member, and then, curing by irradiation with ultraviolet rays or by heating.
Thus, when the gelatinous damping material is applied onto the supporting member as disclosed in the Reference 2, the coating is performed on the plate spring as shown in FIG. 15. However, the coating of the plate spring with damping material inevitablly causes the damping material to flow around the plate spring so as to spread thinner, thereby bringing about the risk that the required performances cannot be obtained. Further, in the Reference 2, no particular consideration is given to the distance between the spring part and the projecting part and so on.
When a supporting member composed of inexpensive linear wires is used instead of the above-mentioned plate spring, only the application of the gelatinous damping material to an edge of the spring without providing the container type structure as disclosed in the Reference 1 also causes the damping material to flow out, so that it is difficult to obtain stable performance. Therefore, in the prior art, it is extremely difficult to obtain an optical system supporting device having a structure desirable not only in terms of controllability but also in terms of minimization and weight reduction by the combination of the gelatinous damping material with the wire as the supporting member.